1. Field of the Invention
The present invention relates to a method of manufacturing a transistor and a method of manufacturing an amplifier.
2. Background Art
There is known a conventional high-frequency nitride semiconductor transistor manufactured by allowing a GaN layer and an AlGaN layer to epitaxially grow on a substrate, forming a source electrode, a gate electrode and a drain electrode thereon and finally providing a nitride film as a protective film (e.g., see D. Marcon et al., “A Comprehensive Reliability Investigation of the Voltage-, Temperature- and Device Geometry-Dependence of the Gate Degradation on state-of-the-art GaN-on-Si HEMTs,” IEEE International Electron Devices Meeting (IEDM), December 2010, p 472).
Although a silicon substrate is used in this transistor, a SiC substrate can also be used to form a transistor provided with a similar laminated structure, electrodes and protective film.
Other prior art includes Japanese Unexamined Patent Application Publication No. 2009-507396, Japanese Laid-Open Patent Publication No. 2012-104760, Japanese Laid-Open Patent Publication No. 2000-174292, Japanese Laid-Open Patent Publication No. 2005-317684, Japanese Laid-Open Patent Publication No. H5-304123, and Japanese Laid-Open Patent Publication No. 2004-31946.
A characteristic variation caused by a gate current has been a problem with the above conventional transistor. With Schottky junction type field-effect transistors (FETs), a certain range of voltage is applied between a gate electrode and a drain electrode so as to produce a reverse potential difference with respect to a Schottky barrier. In this case, electrons flow from the gate electrode into a semiconductor layer and are observed as a gate current.
When actually using this type of transistor in a circuit, a gate resistor may be connected in series to the gate electrode. A typical example of this is a case where the transistor is used for an amplifier. When the gate current is high, a voltage drop in this gate resistor increases. The variation in the gate current may cause the gate voltage to change, resulting in a problem that transistor operation is affected.